Polychromatic zirconia bodies and methods of making the same

ABSTRACT

A ceramic body is provided that is suitable for use in dental applications to provide a natural aesthetic appearance. A colorized ceramic body is formed that has at least one color region and a color gradient region. A ceramic body is formed having at least two color regions and a color gradient that forms a transition region between two color regions. A method for making the colorized ceramic body includes unidirectional infiltration of a coloring composition into the ceramic body.

This application is a continuation of, and claims the benefit of andpriority to, U.S. patent application Ser. No. 16/260,640, filed Jan. 29,2019, which claims the benefit of and priority to U.S. ProvisionalPatent Application No. 62/635,644, filed Feb. 27, 2018 and U.S.Provisional Patent Application No. 62/623,102, filed Jan. 29, 2018, theentireties of each of which applications are incorporated herein byreference.

BACKGROUND

Colorization of porous, millable ceramic blocks is known. Throughconventional processes including dipping, spraying, and painting,coloring liquids may infiltrate pores of a pre-sintered ceramic bodyenhancing the appearance of ceramic material. Colored ceramic blockshave applications as dental restorations, such as crowns, bridges,partial and full dentures. However, conventional colorization methodsthat yield single colored ceramic blocks may be unsuitable for makingdental restorations that match the appearance of natural dentition inwhich color is smoothly variable over the surface.

To achieve the aesthetics of natural dentition in ceramic restorations,attempts have been made to create a polychromatic appearance. Forexample, in some methods pigment is applied by hand-painting; however,the results of the labor-intensive method depend largely on the skill ofthe dental technician. In other conventional methods, batches of ceramicpowder with multiple colors are pressed as individual layers to formmulti-layered blocks, which can be milled into polychromaticrestorations. However, making powder batches with multiple colors andproviding storage may be costly.

A further method attempts to target the distribution of color pigmentsin a porous ceramic by a convection flow. The flow direction andvelocity are regulated by environmental parameter gradients, such as airhumidity gradient, pressure gradient, and/or temperature gradient.Controlled directional movement of color pigment is attempted bychanging the direction of one or more parameters of the convective flow.

SUMMARY

A polychromatic ceramic body suitable for use in dental restorationapplications having a natural appearance is provided. A method formaking the polychromatic ceramic body, and a device for coloring theceramic body, are also provided. In one embodiment, the ceramic bodycomprises a discrete color region, having a uniform color throughout theregion, and a gradient color region adjacent the discrete color region.In another embodiment, a polychromatic ceramic body comprises two ormore color regions arranged from the top surface of the ceramic body tobottom surface (y-axis direction). In a further embodiment, a transitionregion comprising a smooth color gradient is located between two colorregions. Each color region may comprise substantially uniform coloracross the diameter or width of a ceramic body, and the ceramic body maybe any shape, including but not limited to, cylinder, disc, orpolyhedron, such as a cube or prism.

Color regions of a minable ceramic block may be tailored to provide afirst color or shade at a top region of the ceramic block and a secondcolor or shade that is lighter than the first shade at a bottom region.A computer design of a dental restoration, such as a restoration toothor denture design, may be nested so that a cervical and/or body regionis milled from a darker shaded top portion, and an incisal region ismilled from the lighter bottom region. The lighter, bottom region may,optionally, have greater translucency than the top region, creating anatural incisal appearance in a finished dental restoration.Advantageously, a color transition region eliminates sharp boundariesbetween two color regions that may occur in traditional processes. Theresulting dental restorations may comprise a smooth color or shadegradient between the body region and incisal region of a restorationtooth.

A method for making the polychromatic ceramic body comprises theunidirectional infiltration of a liquid coloring composition into andthrough a portion of the porous ceramic body (in the y-axis direction).Prior to infiltration, side surfaces of the ceramic body may be renderedimpermeable to coloring compositions during the infiltration process,thereby restricting the ingress and egress of liquid coloringcompositions through side surfaces, contributing to the unidirectionalmovement of liquid coloring compositions from a top surface to a bottomsurface. In one embodiment, between top and bottom surfaces, curved sidesurface of a ceramic disc or cylinder, or sides and side edges of apolyhedron, are covered with a casing material that is resistant topenetration by the liquid coloring composition during infiltration.Bottom surfaces and edges between bottom and side surfaces, may also becovered to resist the ingress or egress of liquid coloring compositioninto or out of the porous ceramic body from any surface other than thetop surface.

A smooth color gradient may be formed by infiltrating a liquid coloringcomposition into a first portion of a porous ceramic body, fixing (e.g.by heating) a portion of the infiltrated liquid coloring composition atone end of the ceramic body to prevent further infiltration of a portionof the infiltrated liquid coloring composition, and thereby forming acolor region. The remaining (non-fixed) portion of the infiltratedliquid coloring composition may continue to diffuse through thethickness of a second portion of the porous ceramic body forming a colorgradient region adjacent the color region. A color gradient has agreater concentration of coloring agent adjacent the region infiltratedby liquid coloring composition and lesser concentration of coloringagent as the distance from the region increases. In another embodiment,the smooth color gradient may be accomplished by introducing a dilutingliquid within a first region of the ceramic body prior to infiltrating aliquid coloring composition. A smooth color gradient forms as a portionof the liquid coloring composition that has been infiltrated into asecond region, mixes with a portion of the infiltrated diluting liquid,and the diluted coloring composition gradually infiltrates or diffusesfurther into the ceramic body.

In a further embodiment, a porous ceramic body covered by a casingmaterial on side and bottom surfaces is infiltrated by a liquid coloringcomposition that occupies substantially, the entire pore volume of theceramic body. After sintering, a monochromatic body is formed having auniform color throughout the mass of the sintered ceramic body.

In a further embodiment, a method has been made for improvingmachinability of a polychromatic ceramic body. In one embodiment, abisque or partially sintered porous ceramic body that is infiltratedwith a liquid coloring composition is heated to a temperature below thesintering temperature of the ceramic for a period of time, to facilitatemilling of the colorized ceramic body.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of an embodiment of a sectionedpolychromatic body.

FIG. 2 is a perspective view of one embodiment of a ceramic body in acasing with a cut-out of a portion of the casing surrounding the ceramicbody.

FIG. 3 is a cross-sectional illustration of an embodiment of aninfiltration set-up.

FIGS. 4 a and 4 b are cross-sectional illustrations of one embodiment ofan infiltration process and set-up according to the invention.

FIG. 5 is a cross-sectional illustration of an embodiment of aunidirectional infiltration process and set-up for making amonochromatic ceramic body.

FIGS. 6 a and 6 b are cross-sectional illustrations of an embodiment ofa unidirectional infiltration process for making a polychromatic ceramicbody having a color region and a transition region.

FIGS. 7 a, 7 b, and 7 c , are cross-sectional illustrations of anembodiment of a sequential, unidirectional infiltration process formaking a polychromatic ceramic body having a transition region betweentwo color regions.

DETAILED DESCRIPTION

A method is disclosed for providing color to a ceramic body through aninfiltration technique. A ceramic body is provided that has one or morecolor regions, and optionally, a color gradient region. In anotherembodiment, a ceramic body is provided having at least two color regionsand a color gradient region that forms a transition region between twocolor regions. A method for making a polychromatic ceramic body, and adevice for coloring a ceramic body, are disclosed. Single shaded andpolychromatic ceramic blocks are suitable for use in making dentalrestorations, such as ceramic dental restoration teeth and bridges,having a natural appearance.

In an exemplary embodiment, illustrated in FIG. 1 , a polychromaticceramic body (100) comprises two or more color regions (101, 103) and acolor transition region (102) providing a smooth color gradient therebetween. In this embodiment, individual color regions (101, 103) andcolor transition region (102) are arranged from a top surface (104) ofthe ceramic body to a bottom surface (105) along an axis (referred toherein as y-axis direction, as illustrated in FIG. 1 ). A colortransition region (102) provides a gradual transition (illustrated inFIG. 1 by broken lines) between the color of a first region (101) andthe color of a second region (103). As illustrated in FIG. 1 , a colorregion (101, 102, 103) extends between outer side surfaces (106) acrossthe width or diameter (x and z axis direction) of the ceramic body, fora selected height (in the y-axis direction).

The polychromatic ceramic body, illustrated in FIG. 1 as a disc-shapedbody, may be any shape suitable for use in making dental restorations.In one embodiment, a dental restoration crown milled from thepolychromatic ceramic body, comprises a cervical area (e.g., adjacentthe gingiva when installed) and/or a body portion that is milled from adarker color region (101), and an incisal region (e.g. adjacent anincisal edge) that is milled from a lighter color region (103), of theceramic body. The crown comprises a smooth color gradient betweencervical/body region and incisal region shades, providing a naturalappearance.

A method for making the polychromatic ceramic body comprisesunidirectionally, infiltrating a liquid coloring composition into aportion of the porous ceramic body (in the y-axis direction). Prior toinfiltration, the outer side surface (106) is covered with a casing thatextends from the top edge, adjacent the top surface (104), to the bottomedge, adjacent the bottom surface (105). Casing material may prevent theflow of the liquid coloring composition in the x-axis and z-axisdirections by inhibiting ingress and/or egress through the sidesurface(s), and optionally, bottom surface, of the porous ceramic bodyduring the infiltration step.

Where the ceramic body is a ceramic disc or cylinder, the permeationresistant casing material may be in direct contact with the porousceramic surfaces covering the entire curved outer side surface from thetop to the bottom of the ceramic body. Where the ceramic body is apolyhedron, the sides and joining edges may be covered with the casingmaterial. Bottom surfaces (105), and edge(s) between bottom and sidesurfaces, may also be covered by contact with a casing that inhibits theingress or egress of liquid into and/or out of the porous ceramic bodyfrom any surface other than the top surface (104).

A casing suitable for use herein hinders movement of infiltratingliquids into or out of surfaces of the porous ceramic body to which thecasing material is applied, such as liquid coloring composition and/ordiluting liquid. Casing materials may comprise waterproof, waterresistant and/or chemically resistant materials. Suitable materialsmaintain contact with the porous surfaces during infiltration processes,and resist penetration by infiltrating liquids (e.g., liquid coloringcomposition and/or diluting liquid) throughout the infiltration process.For example, casing materials may withstand penetration or chemicaldegradation by acidic liquid coloring compositions during theinfiltration process, preventing the introduction of liquid coloringcomposition into covered portions of the porous ceramic body. Casingmaterials may be applied by conventional processes for covering asurface, including, but not limited to, coating, wrapping, or adheringthe material onto ceramic body surfaces. Flexible or stretchablematerials may be shaped to form a permeation resistant body into whichthe porous ceramic body is inserted. Casing materials suitable for useherein, include, but are not limited to, plastic or rubber materials,and polymeric materials such as polyurethane or fluorinated polymers.

As illustrated by the embodiment in FIG. 2 , a ceramic body (200) iscontained in a casing in which only the top surface (201) is notcovered. A cutaway of the casing is provided for illustrative purposes,demonstrating a side surface (205) of the ceramic body (200) and aninner side wall of the casing material in tight-fitting relationship,preventing liquid components from moving out of, or in through, theceramic body outer surfaces to which it contacts. In one embodiment, thecasing (202) may comprise a flexible or resilient material that bends orstretches to accommodate the ceramic body, surrounding, contacting andconforming to the entire side surface of ceramic body (200) from the topedge to the bottom; a bottom portion (203) of the casing conforms to thebottom surface and a bottom edge to prevent movement of a liquidcoloring solution into or out of the ceramic body through the bottomsurface. The casing side wall (204) may extend above the top surface(201) of the ceramic body to form a reservoir (206) that holds a volumeof liquid coloring composition directly on the top surface (201) of theceramic body during infiltration.

FIG. 3 illustrates a cross-sectioned perspective view of one embodimentof an infiltration set-up (300). A porous ceramic body (301) iscontained within a permeation-resistant casing (302) having a side walland bottom that tightly conforms to the side and bottom surfaces of theporous body (301). In this embodiment, both the casing and the ceramicbody are placed within a container (304) that has an opening (307) forintroducing a volume of liquid coloring composition into theinfiltration set-up, directly onto the top surface of the porous ceramicbody (301), opposition a bottom (305) of the container. The container iscomprised of a material suitable for supporting the casing during theinfiltration process, including, but not limited to, plastic, glass andceramic. The container may be inert, resistant to penetration and/orresistant to degradation, by the liquid coloring composition, a dilutingliquid, or both.

In the embodiment illustrated in FIG. 3 , the side wall of the container(304) and casing (302) extend beyond the top edge of the ceramic bodyand form the reservoir (306) adjacent the infiltration surface (e.g. topsurface) of the porous ceramic body. The liquid coloring composition isheld in the reservoir in contact with the top surface of the porous,ceramic body during the infiltration process. The liquid coloringcomposition infiltrates into an upper region of the porous ceramic bodyadjacent the top surface over a period of time. In one embodiment, theinfiltration depth of the liquid coloring composition is at least 1 mmfrom the top surface, or at least 5 mm from the top surface, or at least10 mm from the top surface, or between 1 mm and 20 mm from the topsurface, or between 5 mm and 14 mm from the top surface, of the ceramicbody. In another embodiment, the infiltration depth of the liquidcoloring composition is in the range of 10% to 95%, or 10% to 100%, ofthe height of the porous ceramic body measured in the y-axis directionfrom an end surface, (e.g. the top surface.) Infiltration may proceedfor a sufficient time for the liquid coloring composition to uniformlyinfiltrate to a desired distance from the infiltration surface. Excessliquid coloring composition that has not been infiltrated may be removedfrom contact with the top surface (303). In one embodiment, infiltratedliquid coloring composition may continue to infiltrate or diffuse,unidirectionally, toward the bottom surface of the ceramic body tooccupy a target region, until the coloring composition is fixed (e.g. byheating). The ceramic body may be heated, fixing metal-containingcomponents of the coloring agent, and inhibiting further diffusion ofthe coloring agent through the ceramic body.

In one embodiment, a first portion of the liquid coloring composition isfixed in an upper region (101) (e.g. by heating) to prevent furtherdiffusion of the fixed portion into the ceramic body. A second portionof the liquid coloring composition that has not been fixed, a non-fixedportion, may continue to diffuse or to infiltrate, unidirectionally,toward the bottom surface of the porous ceramic body. The second portionof the liquid coloring composition may then be fixed to terminatefurther diffusion, fixing the second portion of the coloring compositionbetween the upper region (101) and a lower region (103), and the secondportion may form a color transition region (102) between the upperregion and lower region. The color transition region (102) forms asmooth color gradient lacking discernable color transition lines betweenthe transition region and the upper and lower regions, when viewed withthe unaided eye.

The dimensions of the color regions and color gradient regions may bedesigned to be the same or different. In one embodiment, a first colorregion, a second color region and a color gradient region each compriseapproximately one third of the height (y-axis direction) of a sinteredceramic body, uniformly through the entire width or thickness. Thedimension of the upper region may be controlled, for example, bycontrolling the volume of liquid coloring composition that infiltratesthe upper region. The dimension of the upper region may also becontrolled by the amount of liquid coloring composition that is fixed inthe upper region before further diffusing to form the transition region.The location and dimension of the transition region may be selected bycontrolling the amount of coloring liquid that infiltrates prior tofixing the coloring liquid to form a first color region, and/or bycontrolling the amount of diffusion that occurs prior to a final heatingstep that fixes the coloring agent and terminates further diffusion.

Illustrated in the exemplary embodiment of FIG. 4 a , the ceramic body(400) is contained within a casing (401), and placed in a container(407) to form an infiltration set-up. The ceramic body is illustratedhaving a first region that has been infiltrated by a diluting liquid(402) adjacent a bottom surface (406). A volume of liquid coloringcomposition (403) is contained within a reservoir formed by side walls(405) of the container (407) and the exposed, top surface (404) of theceramic body. The liquid coloring composition (403) infiltrates throughthe top surface (404) in a downward direction into a second region ofthe porous body. In this embodiment, the liquid coloring composition(403) contacts the diluting liquid (402) at an interface between theliquid coloring composition and the diluting liquid. Within the porousceramic body, a portion of the coloring agent of the liquid coloringcomposition diffuses into the diluting liquid forming a continuousgradient as the coloring agent concentration decreases from a lowerportion of the second region that comprises the liquid coloringcomposition to an upper portion of the first region that comprises thediluting liquid.

In the exemplary embodiment of FIG. 4 b , after infiltration anddiffusion of liquid coloring composition, three regions are formed inthe porous ceramic. An upper region (408) of the porous ceramic bodypredominantly contains the liquid coloring composition within the porevolume, and a lower region (409) predominantly contains the dilutingliquid. A transition region (410) is formed between upper and lowerregions upon dilution of a portion of the liquid coloring composition. Asmooth color gradient is formed as the concentration of coloring agentwithin the transition region gradually decreases within the transitionregion.

In a further embodiment, illustrated in FIG. 5 , a colored, ceramic bodyis formed having a uniform color between top and bottom surfacesthroughout the mass of the ceramic body. In this embodiment, a volume ofliquid coloring composition (501) is provided adjacent a top surface(502) that uniformly infiltrates the entire porous ceramic body (500)from the top surface (502) to the bottom surface (503) (as indicated bythe arrows). Prior to infiltration, the porous ceramic body (500) iscovered on side (504) and bottom (503) surfaces by a casing material(505) preventing the passage of liquid through the side surface andbottom surface of the ceramic body. Upon sintering, a monochromaticceramic body is formed, having a single shade from top to bottom, withno color gradient region.

In a separate embodiment, illustrated in FIG. 6 a , a ceramic body (600)is covered by a casing material (605) on side surfaces and bottomsurfaces, and a volume of liquid coloring composition (601) is adjacentan exposed top surface of the porous ceramic body. The ceramic body(600) is infiltrated by the liquid coloring composition (601) whichfills a top region (602) of the porous ceramic body (600). The volume ofliquid coloring composition (601) that contacts the exposed top surface(604) of the ceramic body, infiltrates unidirectionally, in atop-to-bottom direction (as indicated by the arrows). As illustrated inFIG. 6 b , after infiltrating the top region (602), excess liquidcoloring composition is removed from the top surface, and liquidcoloring composition and/or the coloring agent component,unidirectionally infiltrates or diffuses (as indicated by the arrows)into a second region (603) forming a gradient region.

In a further embodiment, illustrated in FIGS. 7 a, 7 b, and 7 c , asequential, unidirectional infiltration process is provided. In thisembodiment, a porous ceramic body (700) is placed within apermeation-resistant casing material (701), wherein a first porousregion (703) is positioned above a second porous region (705). In afirst step, a volume of diluting liquid (702) in contact with anupward-facing (top) surface (707) of a porous ceramic body (700), isunidirectionally infiltrated (as indicated by the arrows) in a downwarddirection into the first porous region (703) of the ceramic body (700).After infiltration, the ceramic body is inverted, so that the firstporous region (703) is below the second porous region (705). The casing(701) is removed from the upward-facing end surface of the second porousregion (705), and downward facing end surface of the first porous region(703) is covered by casing (701).

In a second infiltration step, as illustrated in FIG. 7 b , a volume ofliquid coloring composition (704) in contact with the porous ceramicbody is unidirectionally infiltrated into the second porous region(705). The liquid coloring composition (704) infiltrates downwardtowards the diluting liquid (702) in the first porous region (703), inthe direction of the bottom of the ceramic body. Thus, a sequential,unidirectional infiltration process is provided where in a first step, adiluting liquid is infiltrated into the porous ceramic body in atop-to-bottom direction (y-axis), and upon inverting the porous ceramicbody, in a second step, a liquid coloring composition is infiltratedinto the porous ceramic body in a top-to-bottom (y-axis) direction.

As illustrated in FIG. 7 c , after infiltration of the liquid coloringcomposition (704) into the second porous region (705), diffusion of thecoloring agent and diluting liquid contained within the first porousregion (703) form a transition region (706).

In this embodiment, where the side surface of the ceramic body iscovered with a permeation resistant casing (701), ingress or egress ofthe liquid coloring composition (704) and diluting liquid (702) throughthe side surface of the ceramic body is prevented. Lateral flow (inx-axis and z-axis directions) of the liquid coloring composition withinthe pore volume of the ceramic body is inhibited by unidirectionallyinfiltration. While not wishing to be bound by theory, it is believedthat in some embodiments, rapid convective mixing of liquid coloringcomposition and the diluting liquid is inhibited as the flow of theliquid components into and out of the side surfaces and bottom surfaceof the ceramic body is restricted by a casing material. Where casingmaterial covers the bottom and side surfaces, inhibiting ingress oregress of the liquid coloring composition and diluting liquid into orout of the ceramic body, mixing of the liquid coloring composition anddiluting liquid may occur slowly through diffusion within the porousceramic body.

In an alternate embodiment, a method for infiltrating the porous ceramicbody with two liquid coloring compositions is provided. In oneembodiment, a first liquid coloring composition is infiltrated into afirst porous region, and a second liquid coloring composition isinfiltrated into a second porous region that is opposite the firstporous region. In this embodiment, a first liquid coloring compositionis infiltrated into a first porous region and any excess liquid coloringcomposition that was not infiltrated is decanted. The porous body may beheated adjacent the first porous region to evaporate liquid component ofthe first liquid coloring composition and to fix at least a portion ofthe first liquid coloring composition in the first region. A non-fixedportion of the first liquid coloring composition may infiltrate ordiffuse toward the second region to form a smooth color gradient betweenfirst and second regions. Subsequently, the ceramic body is, optionally,inverted, and the second liquid coloring composition is infiltrated intothe second porous region. Any excess portion of the second liquidcoloring composition that has not infiltrated is decanted, and theporous ceramic body is heated adjacent the second porous region toevaporation liquid component of the second liquid coloring compositionand fix at least a portion of the second liquid coloring composition. Anon-fixed portion of the second liquid coloring composition mayinfiltrate or diffuse toward the first region to form a second colorgradient between first and second regions. In one embodiment, a singletransition region is formed between the first and second porous regionsthat comprises both first and second liquid coloring compositions. In analternative embodiment, two adjacent transition regions are formed fromthe two liquid coloring compositions. In one embodiment, the porousceramic body contains a diluting liquid within a portion of the porevolume, for example, between the first and second color regions. One orboth of the first and second coloring compositions may mix with thediluting liquid to form one or more smooth color transition regions.

The diluting liquid may comprise a polar or non-polar, organic orinorganic solvent, such as water or isopropyl alcohol (IPA), or mixturesthereof, and the solvent may be the same or different as the liquidcomponent of the liquid coloring composition (403). Optionally, thediluting liquid may comprise from 0.0001 wt % to 5 wt %, or 0.01 wt % to5 wt %, of one or more additives. For example, one or more coloringagents may be dispersed, dissolved, or hydrolyzed, as an additive to thediluting liquid. Coloring agents suitable for use as additives includethose coloring agents described herein for use in the liquid coloringcomposition. An additive that imparts antimicrobial properties in thefinal ceramic body, such as a silver-containing component ormolybdenum-containing component, may be added to the diluting liquid.For example, a molybdenum-containing salt such as molybdenum chloride(e.g., MoCl₃, MoCl₄, or MoCl₅), molybdenum-2-ethylhexanoate (Mo[OOCCH(C₂H₅)C₄H₉]₄), ammonium heptamolybdate ((NH₄)₆Mo₇O₂₄.4H₂O),cyclopentadienylmolybdenum(V) tetrachloride (C₅H₅Cl₄Mo), ormolybdenum(VI) oxide bis(2,4-pentanedionate) (C₁₀H₁₄MoO₆) may besuitable for use herein.

In one embodiment, the diluting liquid is infiltrated within porousceramic body, in an amount between 1 vol % and 100 vol % of the porevolume of the porous ceramic body. In another embodiment, dilutingliquid infiltrates between 1 vol % and 99 vol %, or between 3 vol % and97 vol %, or between 5 vol % and 50 vol %, or between 10% and 85%, orbetween 10 vol % and 95 vol %, or between 25 vol % and 85 vol %, orbetween 30 vol % and 80 vol %, or between 40 vol % and 75 vol %, orbetween 33 vol % and 67 vol %, or between 16 vol % and 45 vol %, of thepore volume of the porous ceramic body.

The porous region containing the diluting liquid may be located anywherebetween the upper or lower surfaces of the ceramic body, such as,immediately adjacent the upper or lower surface. In an alternativeembodiment, the diluting liquid may be in a porous region that is spacedat a distance from the upper surface, the lower surface, or both theupper and lower surfaces. In one embodiment, a volume of diluting liquidthat is at least as great as the pore volume of a region to beinfiltrated is provided to the exposed surface of a porous region, andthe porous region is uniformly infiltrated throughout the width orthickness of the ceramic body for a given depth of penetration.

In a further embodiment, a ceramic body is fully infiltrated with adiluting liquid, and then, a portion of the diluting liquid is removedto form a dry porous region for infiltration by the coloringcomposition. In one embodiment, at least 30 wt % of the diluting liquidis removed from the fully filled ceramic body, forming an unfilled ordry porous region for infiltration by the liquid coloring composition,and a region substantially filled with diluting liquid.

The heights (relative to the y-axis) of the one or more color regionsand the color gradient region may be controlled by controlling therelative volumes of diluting liquid and liquid coloring compositionwithin the ceramic body. The time allotted for infiltration and mixingalso may be selected to control the depth of penetration of colorant ineach region and the smoothness of the gradient of the transition regionin the final sintered ceramic body.

A method for infiltrating a porous ceramic body to make a polychromaticceramic body comprises one or more of the following steps: a)infiltrating a porous ceramic body with a diluting liquid; b) removing aportion of the diluting liquid (e.g., by evaporation through heating) toform a first region without a diluting liquid and a second regioncomprising the diluting liquid; c) unidirectionally infiltrating aliquid coloring composition into the first region of the porous ceramicbody; d) contacting the diluting liquid with the liquid coloringcomposition within the porous structure; e) mixing (e.g., by diffusion)a portion of the liquid coloring composition with a portion of thediluting liquid; and f) forming a color transition region between afirst region that contains liquid coloring composition and a secondregion that contains diluting liquid, wherein the color transitionregion comprises a gradient mixture of coloring composition and thediluting liquid. Infiltration and mixing may occur at ambienttemperature and ambient pressure over a period of time, withoutmodifying or adjusting ambient environmental conditions, such astemperature or pressure. After infiltration in the first and secondregions, the ceramic body may be heated to terminate infiltration bydrying a portion of the diluting liquid or liquid coloring composition,or to terminate diffusion by fixing coloring agents.

In one method, diluting liquid infiltrates from about 10% to 85% of thepore volume of the ceramic body, forming the first region containing thediluting liquid and a second region, opposite the first region that isdevoid of, or unfilled with, diluting liquid. After diluting liquid isinfiltrated into the first region, the ceramic body may be inverted,exposing the second surface. Liquid coloring composition may beinfiltrated into the second region of the inverted porous ceramic bodyadjacent a second surface that is opposite the first surface. Afterinfiltrating the second region, liquid coloring composition may furtherpermeate into the ceramic body and mix with the diluting liquid forminga color transition region. Optionally, a portion of the liquid coloringcomposition may be fixed (e.g., b heating) within the second region anda non-fixed portion may mix with the infiltrated diluting liquid to forma color transition region. By infiltrating only a portion of the ceramicbody (i.e., the first region) with diluting liquid, and inverting theceramic body to expose an unfilled region for infiltration by a coloringcomposition, a heating step to evaporate a portion of the dilutingliquid prior to infiltration by the liquid coloring composition may beeliminated.

The liquid coloring composition comprises a coloring agent and a liquidcomponent. The liquid component may form, for example, a solution,suspension or dispersion with a coloring agent, and the liquid componentmay comprise a polar or non-polar solvent, an organic or inorganicsolvent, such as water or IPA, or mixtures thereof. The liquid coloringcomposition may be acidic having a pH of less than 7, basic having a pHgreater than 7, or neutral with a pH of 7.

Coloring agents may comprise metal-containing components, includingmetallic compounds and metallic complexes having one or more metallicelements of transition metals from groups 3-14 on the periodic table ofelements, rare earth metals, or mixtures of transition metals and rareearth metals. A coloring agent may further comprise a metal-containingcomponents having metals or metal ion(s) including but not limited toTb, Cr, Er, Co, Mn, Pr, V, Ti, Ni, Cu and Zn, to provide a coloringeffect. Metallic oxides, or metallic salts containing anions such asCl⁻, SO₄ ²⁻, SO₃ ²⁻, Br⁻, F⁻, NO₂ ⁻, and NO₃ ⁻, may be suitable for useherein. Metal-containing components may be soluble in the liquid, orcomprise sufficiently small ionic particle size to infiltrate the porouslattice structure of the ceramic body. A coloring agent may comprise anitrate, chloride, or acetate.

The liquid coloring composition may comprise between 0.1 wt % and 8 wt%, or 0.1 wt % and 15 wt %, metallic coloring agent, calculated as metalion, based on the total weight of the liquid coloring composition.Alternatively, the coloring composition may comprise between 0.2 wt %and 6 wt %, or 0.2 wt % and 8 wt %, metallic coloring agent, calculatedas metal ion, based on the total weight of the coloring composition.Optional additives may be included such as organic pigments that burnoff during the pre-sintering or sintering process, may be added toconfirm application of the liquid coloring composition to the porousceramic body.

When applied to porous ceramic bodies, liquid coloring compositions mayinfiltrate throughout the thickness, or within a portion, of theporosity. The liquid coloring composition may fully or partiallyinfiltrate a porous ceramic body having interconnected porosity, or mayfully or partially infiltrate a porous ceramic body having discontinuousporosity. After infiltration, the total amount of metal in the sinteredbody contributed by the coloring composition measured as metal ions, maycomprise between 0.02 wt % and 2 wt %, or between 0.027 wt % and 1.6 wt%, or between 0.03 wt % and 1.4 wt %.

Porous ceramic bodies include green stage bodies, and partiallyconsolidated, or pre-sintered, bisque stage bodies, having densitiesbelow full theoretical density of the ceramic sintered form. Ceramicmaterials include, but are not limited to, alumina, zirconia, andmixtures thereof. Zirconia ceramic bodies may comprise between 85 we/0and 100 wt % of a zirconia material, or between 90 wt % and 99.7 wt %zirconia material, and, optionally, minor amounts of other materials,such as alumina. Zirconia ceramic material may comprise approximately 85wt % and approximately 98 wt % zirconia, or stabilized zirconia, basedon the total weight of the zirconia ceramic material, or approximately85 wt % or greater, or approximately 90 wt % or greater, orapproximately 95 wt % or greater, zirconia, or stabilized zirconia,based on the total weight of the zirconia ceramic material.

Stabilized zirconia ceramic material includes both fully and partiallystabilized zirconia. Stabilized zirconia ceramic powder materialsuitable for use herein includes, but is not limited to,yttria-stabilized zirconia commercially available from Tosoh USA.Further, zirconia may be stabilized with approximately 0.1 mol % toapproximately 8 mol % yttria, or approximately 2 mol % to approximately6 mol % yttria, or approximately 2 mol % to approximately 6.5 mol %yttria, or approximately 2 mol % to approximately 5.5 mol % yttria, orapproximately 2 mol % to approximately 5 mol % yttria, or approximately2 mol % to approximately 4 mol % yttria.

Ceramic powder may have substantially uniform particle sizedistribution, for example, an average particle size in a range fromapproximately 0.005 micron (μm) to approximately 1 μm, or fromapproximately 0.05 μm to approximately 1 μm. Examples of ceramicmaterial suitable for use herein also include zirconia described incommonly owned U.S. Pat. No. 8,298,329, which is hereby incorporated byreference in its entirety.

Both shaded and unshaded (white) ceramic bodies may be infiltrated withthe liquid coloring compositions according to the methods describedherein. Pre-shaded ceramic materials include commercially availableminable, ceramic blocks that match a specific target shade or a shaderange, for example, BruxZir® ceramic blocks (e.g., BruxZir® Shaded 16series in target shades matching VITA® Classic shades; GlidewellLaboratories, Irvine, Calif.).

Porous ceramic bodies suitable for use herein include blocks having ashape that includes, but is not limited to, a cube, cylinder, disc,near-net, shape, or a porous body in the shape of a final dentalrestoration. Porous ceramic bodies may be made, for example, by pressingor slip casting ceramic powders, or by automated additive (e.g., 3-Dprinting) and subtractive (e.g., milling) processes, including CADand/or CAM processes. Processes include, but are not limited to, thosedescribed in commonly owned U.S. Pat. Nos. 9,365,459, 9,434,651, and9,512,317, all of which are hereby incorporated in their entirety,herein.

Prior to infiltration by a liquid coloring composition, the porousceramic bodies may be partially densified, for example, by heating orpre-sintering to increase the density to below full theoretical densityof the material. Pre-sintering methods may be conducted in accordancewith manufacturer instructions. In some embodiments, prior toinfiltration pre-sintering proceeds by heating at an oven temperaturewithin the range of 700° C. to 1200° C. for 1 to 2 hours. Porous ceramicbodies include those having a density of 30% to 90%, or 50% to 90%, or40% to 75%, of full theoretical density of the sintered ceramic body,while maintaining sufficient porosity for partial or completeinfiltration of the liquid coloring compositions into the porous ceramicbody. In some embodiments, the porous ceramic body may comprise at least20 vol % porosity, or at least 25 vol % porosity. Alternatively, aporous ceramic body may comprise at least 40 vol %, or at least 60 vol%, or between 20 vol % and 80 vol %, porosity, when measured byArchimedes method.

The porous (e.g., green stage or bisque stage) ceramic body may beinfiltrated with the liquid coloring composition before or after shapinginto a dental restoration form. The ceramic bodies may be shaped, forexample, as a single unit crown, bridge, partial or full denture, basedon the individual requirements of a patient.

A method has been found for improving machinability of a colorinfiltrated ceramic body during a shaping process. In some embodiments,after the infiltration process is complete, and, after the optionalheating step to terminate the diffusion of coloring agents, the topsurface of the resulting infiltrated body has an increased surfacehardness that may result in difficulty of milling or grinding, or resultin damage to the milling tool. In one embodiment, the method furthercomprises a post-infiltration heat treatment step. The color infiltratedporous ceramic body is further heated to a temperature (such as, abisquing temperature) that is below the sintering temperature of theceramic material, and optionally, above the degradation temperature of ametallic salt component of the coloring composition. In someembodiments, the color infiltrated ceramic body may be heated at atemperature between 400° C. and 1200° C., or between 800° C. and 1000°C., for a period of time between about 30 minutes and 15 hours. The oventemperature may be raised and/or lowered slowly during thepost-colorization heat treatment to prevent cracking due to stress atthe interface between the liquid coloring composition infiltrated regionand the non-coloring liquid infiltrated region.

The infiltrated ceramic bodies, optionally heated in a post-infiltrationheat treatment step, may be milled into the shape of a dentalrestoration reducing damage to the milling tool. The bisque, milledceramic bodies are heated in a final sintering step to eliminateresidual porosity. Ceramic bodies prepared by the methods disclosedherein may be sintered in accordance with instructions of themanufacturer of commercially available ceramic bodies, or by heating ata temperature, for example, between about 1300° C. and 1600° C., forabout 2 hours to 48 hours.

In another embodiment, ceramic material infiltrated with liquid coloringcomposition may be sintered prior to milling into a dental restoration,to provide single shaded or polychromatic, minable sintered ceramicbodies. Ceramic materials that are infiltrated and sintered prior tomilling may have a net shape or size that fits most dental restorationswhile eliminating excess material for removal. Examples of suitableshaped forms which may be sintered to full theoretical density prior toshaping may be found in commonly owned U.S. Patent Publication No.2013/0316305, and U.S. Pat. No. D769,449, both of which are herebyincorporated herein in their entirety.

Sintered ceramic bodies made in accordance with unidirectionalinfiltration methods have a natural polychromatic appearance whilemaintaining sufficient strength suitable for use in anterior andposterior dental applications, as well as full- and partial-archdentures and bridges. One or more color regions of the final sinteredceramic bodies may, optionally, correspond to a bleached shade, or aclassical shade, for example, corresponding to a Classical A1 to D4Vita® shade guide.

Test Methods

Flexural Strength Test—3-Point Bend Strength

Flexure tests were performed on sintered materials using theInstron—Flexural Strength following ISO 6872 for preparation of strengthtesting for dental ceramic. Flexural strength bars were milled andprepared. Once prepared, the bars were placed centrally on the bearersof the test machine so the load applied to a 4 mm wide face was along aline perpendicular to the long axis of the test piece. Then force isapplied and the load needed for breaking the test piece (loading ratewas 0.5 mm/min) was recorded. The flexural strength is calculated usingsample's dimensional parameter and critical load information.

Flexural strength, σ, in MPa was calculated according to the followingformula:

$\sigma = \frac{3\;{Pl}}{2\;{Wb}^{2}}$

where P is the breaking load, in newton; I is the test span(center-to-center distance between support rollers), in millimeters; wis the width of the specimen, i.e. the dimension of the side at rightangles to the direction of the applied load, in millimeters; b is thethickness of the specimen, i.e. the dimension of the side parallel tothe direction of the applied load, in millimeters. The mean and standarddeviation of the strength data was reported. Means should equal orexceed the requirements.

Test bars were prepared by cutting bisque materials taking intoconsideration the targeted dimensions of the sintered test bars and theenlargement factor (E.F.) of the material, as follows:

-   -   starting thickness=3 mm×E.F.;    -   starting width=4 mm×E.F.; and    -   starting length=55 mm×E.F.

The cut, bisque bars were sintered and flexural strength data wasmeasured and calculated according to the 3 point flexural strength testdescribed in ISO (International Standard) 6872.

Density

The density strongly depends on the composition and structure of thesamples of the ceramic materials. Density calculations for ceramicbodies may be determined by liquid displacement method of Archimedesprinciple. Distilled water was used as the liquid medium. Density ofceramic samples were calculated using the following formula:

$\rho = \frac{\left( {W^{2} - W^{1}} \right)}{\left( {W^{4} - W^{1}} \right) - \left( {W^{3} - W^{2}} \right)}$

-   -   ρ=Density (gram/cc);    -   W¹=Weight of empty specific gravity bottle (gram);    -   W²=Weight of specific gravity bottle with sample (gram);    -   W³=Weight of specific gravity bottle with sample and distill        water (gram);    -   W⁴=Weight of specific gravity bottle with distill water (gram).

EXAMPLES

Preparation of Bisque Stage Zirconia Blocks

Porous, bisque-stage, ceramic, zirconia blocks suitable for use indental restoration applications were formed from yttria-stabilized,zirconia ceramic powder as follows. Bisque stage blocks were preparedusing a slip casting method. The yttria-stabilized zirconia powder and adispersant were added to deionized water to form a slurry having asolids concentration of from about 69 vol % to 80 vol % solids. Theslurry was mixed for approximately 5 minutes using a high-shear mixer,then added to the mixing tank of a horizontal bead mill. Horizontal beadmilling was performed on the slurry at a rate of from about 6 to about16 kg dry mass per hour to obtain a slip for slip casting. Aftermilling, the slurry was drained from the mixing tank of the horizontalbead mill and passed through a 20 μm sieve to remove milling media.

The slip obtained from the horizontal bead mill was cast into molds toform cast blocks. A mold was used to form disk shaped blocks having asize of 98 mm diameter×15 mm thickness. After casting, the blocks wereplaced in a dryer at ambient temperature and weighed at 12 hourincrements until the weight of the block had stabilized to form greenbody blocks. Dry green body blocks were loaded into an oven where theblocks were bisque fired at a final hold temperature of 950° C. for ahold time of two hours to form bisque stage ceramic blocks.

Example 1

A polychromatic zirconia ceramic body having two color regions separatedby a smooth color transition region was prepared by unidirectionalinfiltration of liquid coloring composition into a porous zirconiaceramic body prior to sintering.

A liquid coloring composition was prepared by dissolving 17.54 g ofmetallic salts (wherein the metallic salts comprised the metals of Tb,Cr, Er, and Co) in 150 ml of a 35 vol % deionized (DI) water to 65 vol %IPA solution.

A bisquestage, porous, yttria-stabilized zirconia ceramic block,prepared by the slip-casting process as described above and heated in abisquing stage, was soaked in water as a diluting liquid for about 90minutes to completely infiltrate the porous ceramic body with about 45.5g water. The bisque-stage ceramic block was partially dried by heatingon the top surface to eliminate water from the upper region of theporous ceramic block to provide space for infiltration by the liquidcoloring composition, while maintaining a portion of the water in alower region.

The bisqued ceramic block was placed in a polyurethane casing thatconformed to side and bottom ceramic block surfaces, leaving only thetop surface exposed. The casing was comprised of a material which wasresistant to penetration of the coloring composition for the duration ofthe infiltration process. The polyurethane casing with the bisqueceramic block was placed in a plastic container of an infiltrationset-up made substantially according to FIG. 3 .

The liquid coloring composition was introduced into the plasticcontainer which formed a reservoir for the liquid coloring compositionon the exposed top surface of the porous bisqued ceramic block. Theliquid coloring composition was allowed to contact and infiltrate thetop surface of the porous ceramic between three and five hours atambient temperature and pressure. A portion of the coloring compositioninfiltrated the upper region of the ceramic block was mixed with, anddiluted with, remaining water within the porous structure. Excesscoloring composition was removed from the infiltration set-up, and theinfiltrated ceramic block was held for an additional period of betweentwo and five hours at bench-top. The infiltrated block was removed fromthe infiltration set-up and polyurethane casing. Infiltration wasunidirectional, from the top surface into the upper region and towardthe bottom surface of the porous bisque ceramic block. No coloringcomposition permeated through the casing to enter or exit the sidesurface of the porous ceramic block, and no coloring compositionpermeated into or out of the bottom surface of the porous ceramic block.

The color-infiltrated, bisque-stage porous ceramic block was dried toremove the liquid component of the coloring composition and dilutingliquid, and then heated at an oven temperature between 700° C. and 1000°C. for 1 hour.

The dried, bisque ceramic block was milled into the shape of a dentalcrown, wherein the incisal part was milled from the lower regionproximate the bottom surface of the block, and the cervical region ofthe crown was milled from the upper region proximate the top surface ofthe block; the milled shape was sintered to full density between 1450°C. and 1550° C. for about 2 hours.

The resulting polychromatic sintered dental crown comprised two colorregions and a smooth color transition region between the first andsecond color regions. Upper region of the sintered crown comprised about50 percent of the crown height, the transition region comprised about 30percent of the crown height, and the lower region comprised about 20percent of the crown height. The transition region had a smooth colorgradient without sharp boundaries between the two color regions.

Example 2

A polychromatic sintered ceramic block was prepared from a ceramicpowder comprising yttria stabilized zirconia material that was pressedand heated to form a porous, bisque-stage ceramic block.

The coloring solution was prepared by dissolving 9.4 g of metallic salt(wherein the metallic salts comprised the metals of Tb, Cr, Er, and Co)into 50 ml of IPA.

The dry, porous, bisque-stage, ceramic block was placed in apolyurethane casing that conformed to side and bottom surfaces, and thenplaced within an infiltration set-up substantially according toExample 1. No diluting liquid was added to the bisque-stage, ceramicblock prior to infiltration with the coloring solution. Infiltration wasat ambient temperature with coloring solution for 1 hour and 30 minuteswithout the addition of pressure. After infiltration, the excesscoloring solution was removed from the infiltration set-up. Theinfiltrated block was removed from the infiltration set-up and casing,dried for 30 minutes at 85° C. and then sintered at 1550° C. for 6hours.

The sintered polychromatic block showed uniform color infiltrationforming a first color region adjacent a second color region thatcorresponded to the original block color. There was no color gradientregion between the infiltration color and block color regions that wasdetectable with the unaided eye, thus, the polychromatic block lacked asmooth color transition zone between the two color regions.

Example 3

A polychromatic ceramic body was prepared by unidirectional infiltrationof liquid coloring composition into a bisque-stage, porous, zirconiaceramic block prior to sintering.

An yttria-stabilized, bisque-stage, ceramic zirconia body was preparedby a slip-casting technique as described above. The bisque-stage,ceramic zirconia body was inserted in a polyurethane casing and aninfiltration set-up substantially according to Example 1.

A liquid coloring composition formed substantially in accordance withExample 1, was allowed to infiltrate the bisque-stage, ceramic zirconiabody between three and five hours at ambient temperature and pressure.The liquid coloring composition infiltrated to fill a porous regionextending for only a portion of the height of the block. No dilutingliquid was infiltrated into the block prior to infiltration by theliquid coloring composition. Excess liquid coloring composition wasremoved from the infiltration set-up, and the infiltrated ceramic blockwas held for an additional period between two and five hours atbench-top. After holding at bench top, the infiltrated ceramic block wassubsequently heated. The top surface of the infiltrated ceramic blockwas heated to dry and to fix coloring agents of the coloring compositionthat infiltrated near the top surface. Part of the metallic saltcomponent which was not fixed in position by the heating step continuedto infiltrate through a portion of the infiltrated ceramic block. Thecolor-infiltrated ceramic block was then heated at an oven temperaturebetween 700° C. and 1000° C. for about one hour.

A dental crown was milled from the heat-treated infiltrated, ceramicblock, wherein the cervical area was milled from the region near the topsurface and the incisal/occlusal edge was milled from a region near thebottom surface of the ceramic block. The dental crown was sinteredbetween 1450° C. and 1550° C. for about two hours. The sintered dentalcrown had a darker color region in the tooth body area and toothcervical area of the crown, a lighter color region near theincisal/occlusal edge, and a color transition region between the darkerand lighter color regions. The color transition region was gradual andsmooth, having no sharp color boundaries appearing between the colorregions.

Examples 4 and 5

Coloring solution was unidirectionally infiltrated into green andbisque-stage, porous, zirconia, ceramic blocks to form polychromaticceramic bodies.

Yttria-stabilized zirconia, porous, green and bisque stage, disc blockswere prepared substantially according to the slip-casting methoddescribed above. The porous, green and bisque blocks were placed inpolyurethane casings that covered the side and bottom surfaces, and thenthe blocks were placed in an infiltration set-up substantially accordingto Example 1.

A coloring solution was prepared by dissolving 9.4 g of metallic salt(wherein the metallic salts comprised the metals of Tb, Cr, Er, and Co)into 50 ml of IPA.

Half of the green bodies and half of the bisque-stage porous ceramicblocks were infiltrated by the coloring solution at ambient temperatureand without the addition of pressure for 15 hours. Half of the greenblocks and half of the bisque-stage porous ceramic blocks wereinfiltrated by the coloring solution at ambient temperature under 40 psipressure for 15 hours. Pressure infiltration at 40 psi was conductedafter putting the whole infiltration setup into a pressure chamber (BegoWiropress SL Pressure Vessel). For all infiltration processes, no wateror other diluting liquid was infiltrated into the blocks prior toinfiltration by the coloring solution. After infiltration by thecoloring solution, all blocks were dried in the oven at 90° C. for 30min. After drying, the infiltrated blocks were sintered between 1450° C.and 1550° C. for two hours.

All sintered, infiltrated blocks showed uniform color infiltrationthroughout the ceramic mass, forming an upper color region, and anadjacent lower color region that corresponded to the original blockcolor. The infiltrated blocks did not show smooth color transition zonesbetween the upper and lower color regions. No noticeable infiltrationdifference between “no pressure” and “40 psi” for both “green sample”and “bisque sample” was observed. Coloring solution infiltrated muchdeeper into “bisque sample” than into “green sample”.

Example 6

A polychromatic ceramic body was prepared by unidirectional infiltrationof a coloring solution into a bisque stage, porous zirconia ceramic bodyprior to sintering.

An yttria-stabilized zirconia bisque block having thickness of 15 mm wasprepared substantially according to the slip-casting method describedabove. The porous bisque block was placed in polyurethane casing thatcovered and conformed to the side and bottom surface, and then, theceramic block was placed in an infiltration set-up substantiallyaccording to Example 1.

A coloring solution was prepared by dissolving 6.26 grams of metallicsalt (wherein the metallic salts comprised the metals of Tb, Cr, Er, andCo)] into 50 ml of IPA.

The bisqued block was infiltrated with the coloring solution betweenthree and five hours without prior infiltration with water or otherdiluting liquid. Excess coloring solution was decanted from the top ofthe block. The block was held at ambient temperature on the benchbetween two and five hours, and then dried in the oven at 90° C.

The dried block was removed from the infiltration set-up and casing, andthen bisqued between 700° C. and 1000° C. for one hour. Twenty-oneidentical teeth were milled from different locations at the samevertical distance relative to the top surface of the block, and weresintered between 1450° C. and 1550° C. for 2 hour.

Colorization was uniform among all 21 teeth, with all 21 teeth havinguniform, identical color regions, and identical smooth color transitionregions, demonstrating uniform infiltration of the coloring solutioninto the thickness of the whole block, throughout the color regions andtransition region.

Examples 7-9

A polychromatic ceramic body was prepared by unidirectional infiltrationof a coloring solution into a bisqued, porous, zirconia ceramic bodyprior to sintering.

An yttria-stabilized, zirconia, bisque block having thickness of 15 mmwas prepared substantially according to the slip-casting methoddescribed above. The porous, bisque, block was placed in polyurethanecasing that covered and conformed to the side and bottom surfaces, andthen was placed in an infiltration set-up substantially according toExample 1.

A coloring solution was prepared by dissolving 6.26 grams of metallicsalt (wherein the metallic salts comprised the metals of Tb, Cr, Er, andCo) into 50 ml of IPA.

Deionized (DI) water, as a diluting liquid, was infiltrated into porous,bisque, block for 1 hr. 30 min. followed by drying between two and fivehours to remove a portion of the infiltrated diluting liquid. The driedblock was infiltrated with coloring solution between three and fivehours. Excess coloring solution was decanted, and then, the block washeld on the bench between two and five hours at ambient temperature. Theblock was dried at 90° C. for 30 minutes, and then was bisqued between700° C. and 1000° C. for an hour. After the bisquing, two different setsof samples were milled from two different locations of the infiltratedblocks. The first set of samples was milled from the main body colorzone, and the second set of samples was milled from the transition zone.The third set of samples was milled from the white, non-infiltratedyttria-stabilized zirconia zone. All three sets of samples were sinteredbetween 1450° C. and 1550° C. for two hours, and then mechanicallytested for 3-point bend strengths.

Eight to ten bend bars were prepared from each of the three sets oftesting samples. The 3-point bend strengths of the non-infiltratedsamples, transition-colored samples, and main body-colored samples were825±136 MPa, 868±46 MPa, 800±96 MPa, respectively, indicate thatmechanical strength was not affected by infiltration of different levelsof coloring solution.

Examples 10-13

Polychromatic zirconia ceramic bodies were prepared by unidirectionalinfiltration of liquid coloring compositions into a porous zirconiaceramic body.

Liquid coloring compositions were prepared by dissolving approximately30 g to 40 g of metallic salts (wherein the metallic salts comprised themetals of Pr, Cr, Er, and Co) in approximately 150 ml to 250 mldeionized (DI) water. Diluting liquids were selected from eitherdeionized water having no coloring component, or a solution comprisingapproximately 18.4 g of the above-listed metallic salts, as a colorant,dissolved in 150 ml to 250 ml of deionized water.

Porous yttria-stabilized zirconia ceramic blocks were prepared. Thedisc-shaped blocks two having the dimension of 18 mm thickness and 98 mmdiameter, and two having a thickness of 31.5 mm and 98 mm diameter, hadporosities in the range of 50 vol % to 65 vol % after heating in abisquing stage. Side surfaces were covered with casing material duringinfiltration processes. The end surface of each block was not coveredwhen in an upwardly facing position for infiltration, leaving it exposedfor infiltration of diluting liquid or coloring compositions throughthis surface. The end surface of each block were covered in casingmaterial when in a downwardly facing position during infiltration toprevent the infiltrating liquids from penetrating through the bottom ofthe ceramic block.

Examples 10 and 11

Two of the ceramic disc-shaped blocks described above (18 mm thicknessand 98 mm diameter) were infiltrated through exposed upwardly facingsurfaces. One block (Ex. 10) was infiltrated with 100 ml-250 mldeionized water for 2 minutes to 5 minutes; the second block (Ex. 11)was infiltrated with diluting liquid with colorant for 2 minutes to 5minutes. The blocks were inverted, and infiltrated with a coloringsolution for 10 minutes to 90 minutes. After infiltration with coloringliquid, the blocks were held at the bench for 20 minutes to 120 minutesat ambient temperature, then dried at 120° C. for 30 minutes beforeheating to a bisquing temperature between 700° C. and 1000° C. for twohours. After bisquing, one three-unit bridge and one single tooth weremilled from each block, and sintered between 1450° C. and 1550° C. fortwo hours.

The sintered teeth of the three-unit bridges and each individual toothhad a darker shaded upper body region and a lighter shaded incisalregion with a smooth color transition region there between. The shade ofthe color transition region decreased in intensity between the bodyshade and the incisal shade regions, with no sharp distinguishabletransition lines between the regions. For the restorations milled fromthe ceramic block in which water was used as the diluting liquid (Ex.10), the shade of the incisal regions matched the shade of the sintered,original block material; for the restorations milled from the ceramicblock infiltrated with a diluting liquid having a colorant (Ex. 11), theshade of the cervical and body regions were darker than the sintered,original unshaded ceramic block.

Examples 12 and 13

Two ceramic blocks described above (disc-shaped, 31.8 mm thickness and98 mm diameter) were infiltrated through exposed upwardly facingsurfaces with the diluting liquid having a metal colorant. One ceramicblock (Ex. 12) was infiltrated with diluting liquid for 1 minutes to 3minutes; the second ceramic block (Ex. 13) was infiltrated with thediluting liquid for 9 minutes to 15 minutes. After infiltration bydiluting liquid, the blocks were inverted and the opposite end surfaceswere infiltrated with a liquid coloring solution. The block of Ex. 12,was infiltrated with coloring solution for 10 minutes to 30 minutes; theblock of Ex. 13 was infiltrated with coloring solution for 30 minutes to120 minutes. After infiltration with liquid coloring solution, theblocks were held at the bench for 20 minutes to 120 minutes at ambienttemperature, then dried at 120° C. for 30 minutes, before bisquingbetween 700° C. and 1000° C. for one hour. After bisquing, the blockswere sintered between 1450° C. and 1550° C. for two hours.

For the infiltrated ceramic block of Ex. 12, a cross-sectional viewafter sintering revealed three distinct regions: a dark color regionadjacent one end surface, a lighter color region adjacent the oppositeend surface, and a middle region. The middle region had a colorconsistent with the unshaded ceramic block indicating the coloringsolution and/or diluting liquid did not penetrate this region. Sharptransition lines appeared between the dark color region and the middleregion, and there was no color gradient region between the two colorregions. The sharp transition lines and lack of color gradient indicatedan insufficient amount of infiltration to enable dilution of thecoloring agent of the liquid coloring solution by the diluting liquid tooccur.

For the block according to Ex. 13, a cross-sectional view of thesintered body showed a dark color region adjacent one end surface, alighter color region adjacent the opposite end surface, and a smoothtransition region in between the two color regions. The transitionregion's color decreased in intensity from the dark color region to thelighter color region. No sharp or noticeable transition lines occurredbetween the color regions and the transition region, indicating that theinfiltrated liquid coloring solution came in contact with theinfiltrated diluting liquid, and the coloring agent of the liquidcoloring solution was diluted by the diluting liquid to form the colortransition region.

We claim:
 1. A method of coloring a ceramic body for use in dentalapplications comprising: a. obtaining a porous ceramic body comprisingi. a first end surface adjacent a first porous region, ii. a second endsurface adjacent a second porous region, opposite the first end surface,and iii. a side surface that extends between the first end and secondend surfaces; b. infiltrating a diluting liquid through the first endsurface to occupy a first porous region adjacent the first end; c.preventing the diluting liquid from passing through the second endsurface and the side surface; d. infiltrating a liquid coloringcomposition comprising a liquid component and a coloring agent throughthe second end surface to occupy the second porous region adjacent thesecond end surface, e. preventing the liquid coloring composition andthe diluting liquid from passing through the first end surface and sidesurface; f. contacting a portion of the liquid coloring composition inthe second porous region with a portion of the diluting the dilutingliquid in the first porous region; and g. forming a color gradientregion, wherein the coloring agent has a concentration that decreasesfrom the second porous region towards the first porous region.
 2. Themethod of claim 1, wherein the liquid coloring composition contacts thediluting liquid at an interface and the coloring agent is diluted by thediluting liquid adjacent the interface.
 3. The method of claim 1,wherein during infiltrating the diluting liquid, the first porous regionis positioned above the second porous region, and the diluting liquid isinfiltrated into the ceramic body through the first end surfacedownwardly into the first porous region.
 4. The method of claim 3,further comprising inverting the porous ceramic body after infiltratingthe diluting liquid to position the second porous region above the firstporous region, and the liquid coloring composition is infiltrated fromthe second end surface downwardly into the second porous region.
 5. Themethod of claim 1, comprising unidirectionally infiltrating the dilutingliquid from the first end surface into the first porous region, andunidirectionally infiltrating the liquid coloring composition from thesecond end surface into the second porous region, wherein the dilutingliquid and the liquid coloring composition are infiltrated sequentially.6. The method of claim 1, comprising infiltration between 3% by volumeand 75% by volume porosity of the porous ceramic body with the dilutingliquid, and infiltrating between 25% by volume and 97% by volumeporosity of the porous ceramic body with the liquid coloringcomposition.
 7. The method of claim 1, further comprising heating theporous ceramic body to fix a first portion of the coloring agent in aposition within the porous ceramic body, and for a second portion of thecoloring agent that is not fixed, diffusing the second portion withinthe porous ceramic body.
 8. The method of claim 1, wherein the dilutingliquid comprises a solvent selected from a polar or non-polar solvent.9. The method of claim 1, wherein the liquid coloring compositioncomprises at least one metallic salt as a first coloring agent.
 10. Themethod of claim 9, wherein the diluting liquid comprises a secondcoloring agent.
 11. The method of claim 10, wherein the second coloringagent of the diluting liquid has a metallic salt concentration that isless than a metallic salt concentration of the first coloring agent inthe liquid coloring composition.
 12. The method of claim 1, wherein theporous ceramic body is a zirconia ceramic body.
 13. The method of claim1, comprising fully infiltrating the porous ceramic body with thediluting liquid and removing a first volume of the diluting liquid fromthe porous ceramic body, wherein a second volume of the diluting liquidoccupies the first porous region.
 14. A method of coloring a ceramicbody for use in dental applications, comprising: a. positioning a porousceramic body within an enclosure of an infiltration apparatus, whereinthe porous ceramic body comprises a side surface, a first end surfaceadjacent a first porous region, and a second end surface adjacent asecond porous region opposite the first end surface; b. providing avolume of a diluting liquid within the enclosure on the first endsurface of the porous ceramic body; c. infiltrating the diluting liquidthrough the first end surface of the ceramic body into a first porousregion of the porous ceramic body; d. preventing the diluting liquidfrom passing through the second end surface and the side surface of theporous ceramic body; e. inverting the porous ceramic body within theenclosure; f. providing a volume of a liquid coloring compositioncomprising a liquid component and a coloring agent within the enclosureon the second end surface; g. infiltrating the liquid coloringcomposition through the second end surface into a second porous regionthat is adjacent the first porous region; h. preventing the dilutingliquid and liquid coloring composition from passing through the firstend surface and the side surface of the porous ceramic body; i.contacting a portion of the liquid coloring composition in the secondporous region with a portion of the diluting liquid in the first porousregion, and then mixing to form a color gradient region having aconcentration of coloring agent that decreases from the second porousregion to the first porous region; j. optionally, drying the infiltratedceramic body, and bisquing, the infiltrated porous ceramic body; k.optionally, shaping the infiltrated porous ceramic body; and l.sintering to form a sintered ceramic body comprising a first colorregion adjacent a first end surface, a second color region adjacent thesecond end surface, and a color gradient region there between.
 15. Themethod of claim 14, comprising unidirectionally infiltrating thediluting liquid from the first end surface into the first porous region,and unidirectionally infiltrating the liquid coloring composition fromthe second end surface into the second porous region, wherein thediluting liquid and the liquid coloring composition are infiltratedsequentially.
 16. The method of claim 14, wherein when the porousceramic body is positioned in the infiltration apparatus, the firstporous region is above the second porous region and the diluting liquidis infiltrated from the first end surface downwardly into the firstporous region, and upon inverting the porous ceramic body, the secondporous region is above the first porous region and the liquid coloringcomposition is infiltrated from the second end surface downwardly intothe second porous region.
 17. The method of claim 14, wherein a totalvolume of liquid coloring composition and diluting liquid provided tothe enclosure is greater than a total pore volume of the porous ceramicbody.
 18. The method of claim 14, wherein the color gradient regioncomprises a smooth color transition between the first and second colorregions upon sintering the porous ceramic body.
 19. A method of coloringa ceramic body for use in dental applications comprising: a. obtaining aporous ceramic block for use in machining a dental restorationcomprising i. a first end surface adjacent a first porous region, ii. asecond end surface adjacent a second porous region, opposite the firstend surface, and iii. a side surface that extends between the first andsecond end surfaces; b. providing a volume of a liquid coloringcomposition comprising a liquid component and a coloring agent directlyabove the second end surface, c. infiltrating the liquid coloringcomposition downwardly into the second porous region; d. fixing a firstportion of the liquid coloring composition in the second porous regionby heating; and e. diffusing a second portion of the liquid coloringcomposition that was not fixed in the heating step into the first porousregion forming a color gradient region in the first porous region.